Bump debhelper version to 8 (was 7.0.1); update debian/compat.
* Update debian/rules:
  - switch from cdbs to dh
  - use hardening flags in compiler options
  - add -Wl,--as-needed to LDFLAGS
Add debian/patches/add-hardening-flags-in-compiler-options.
Update years in debian/copyright.
Update debian/changelog.